In general, compounds having a perfluoroalkyl group as a structural unit are known to improve surface modifying properties, water- and oil-repellency, mold releasability, antifouling properties, leveling properties, etc., of various substrates, such as fiber, metal, glass, rubber, and resin, by chemical treatment of the surface of each substrate.
Among such compounds, telomer compounds containing a perfluoroalkyl group having 8 to 12 carbon atoms are most likely to exhibit the above properties. Telomer compounds having 8 carbon atoms are preferably used.
However, it has been recently reported that perfluorooctanoic acid having 8 carbon atoms or perfluorocarboxylic acids having more than 8 carbon atoms have adverse effect on the environment, because they have low degradability and high bioaccumulation potential, and there is suspicion of biological toxicity. Among these compounds, those containing a perfluoroalkyl group having more than 8 carbon atoms are suggested to be possibly converted to perfluorooctanoic acid or perfluorocarboxylic acids having more than 8 carbon atoms by biodegradation or chemical degradation in the environment, and there is concern that it will become difficult to produce and use those compounds for the future. However, compounds containing a perfluoroalkyl group having 6 or less carbon atoms are said to have low bioaccumulation potential.
Fluorine-containing alkylsilane compounds containing a perfluoroalkyl group having 6 or less carbon atoms and having a high water contact angle are also known.
Patent Document 1 discloses a method for obtaining a fluorine-containing alkylsilane compound having terminal —CH2CH2Si(R1)3-nXn by reducing, with a reducing agent, a compound obtained by an addition reaction of RF(CH2CH2)a(CH2CF2)b(CF2CF2)cI with CH2═CHSi(R1)3-nXn.
In this method, however, iodine is desorbed in the final step, and there is thus a concern about coloring of the target compound with iodine. In addition, there is a problem that hydrogenated tributyltin and the like that have a high environmental load are used in the deiodination reaction. Moreover, it is described that a compound having a CH2 group between a CF2 group and a CF2 group is weak under basic conditions, which means that the reaction conditions (synthetic route) are limited.
Patent Document 2 indicates that silane coupling agents having a biphenyl alkyl group Rf(C6H4—C6H4)CH2CH2CH2Si(OCH)3 are compounds having excellent heat resistance, durability, mold releasability, and antifouling properties, so that the contact angle of surfaces modified by these compounds are not reduced even after exposure to an atmosphere at a high temperature of 350° C. or more.
However, these compounds are solids at ordinary temperature because of the biphenyl skeleton in their molecules, and may be thus difficult to handle. Further, organic lithium, such as n-butyllithium, is used as a reaction reagent. This is a highly reactive and water-prohibiting regent. It is thus necessary to slowly drop such a reagent under low temperature conditions, since, for example, control of the reaction heat during the reaction becomes necessary. Thus, handling properties are poor, and the process used therein is not suitable for large-scale production.
A fluorine-containing alkylsilane compound having a bifunctional organosiloxane group is described in Patent Document 3.